i agree with wayner.
i have been using fibreglass tape embedded in dry wall mud for years.
never had a problem.
if the mud is spread correctly, there should be almost zero sanding. scrape the ridges, scuff and prime.

Durabond 90 or 60, and then light skim over with drywall compound. Durabond does not sand easily so don't fill too high.

+1

Important. Smooth and even the Fixall as much as possible when applying. Even little ripples will be a PITA to sand away.

I use paper sheetrock tape and an inside corner tool. Gave up using the mesh tape because it often shows through when sanding - have to be much more careful sanding than with the old fashioned paper tape.

Drywall Tips from the Pros - Extreme How To

Fixall, but keep it below the final float surface, an it doesn't sand. The other product that also hardens chemically is a wood putty called Rockhard, which does sand well, but will cost more.

Light weight topping or mud is very easy to sand anything else, not so much. We sand all our drywall. My drywaller skim over almost everything so we know its dead nuts. Not acceptable to have blemishes. Now, when my men do drywall, we have a dustless drywall sander. Its 95% dustless. this tool is worth its weight in gold. I am the bad guy that cover people's home in dust when ever we are there. That thing makes us look good.

I respectfully disagree.
Product data:
https://www.usg.com/content/usgcom/en_CA_west/products-solutions/products/finishes/joint-compounds/synko-concrete-fill-drywall-compound.html

Apparently the workability has improved since I last used it.

Is Fixall the same ting as Fix-It-All?

Custom Building Products Fix-It-All 25 lb. Patching Compound-DPFXL25 - The Home Depot

Sprayfoam, non expanding to fill the gap, cut off after dry with a sharp knife, and fiberglass tape/spacke over it.

Or I'd put up crown molding.

I would likely do both as properly sealed drywall is a good safety feature Especially if adjoining a garage or near a furnace or where a car runs (outside) to keep out carbon monoxide and slow down fires. Crown molding saves you from having to be perfect in application and would look great on a home from that era.

In rental applications at least, a firebreak such as the special orange 3M foam/caulk and/or rockwool is required between adjoining units (such as sink pipe penetration and basement corners).

Make sure there is a steel door to an attached garage and the wall has a sealed firebreak.

Well, cutting to fit. that's just silly. :D

There are two issues. First issue is the starter piece I installed. 10 foot section of fire-code on the ceiling. Two guys straining to get it in place. That's when I found that I should have measured every angle and trimmed before installing. Piece intersects with three walls. That's the bulk of the gaps. Rigor increased after that one and things tightened up.

Second is trying to cut lath and plaster in a straight line to meet up with another new piece. It likes to come out in chunks. Even though skimming with 1/4" drywall, the new facing is like tissue paper so need to get something behind it, even if a piece of half inch roughly cut and liquid nailed to the lath, held in for starters with a drywall screw.

Wow. Thanks for the info to all.

I did get durabond in a 20 lb bag last night. Maybe the Fixall is a regional thing. Have not tried it yet. I think it's what I need. Fixall probably close to the same product?

The 20 minute set is nice just mix small batches and be ready to use it. When it says 20 minutes, it's not kidding. I've used the 20 and 45 minute for drywall work before. It will actually setup in water. I've used 45 and 90 minute to finish before, you just have to mix it right. It doesn't sand all that bad, just use thin coats so you don't have to sand a much.

This could work nicely.

Nice work with respect to the pic.

Actually, the best way for you to fill those cracks would be to get a couple cases of Great Lakes Porter and a spare bed and have me come do it. Anything short of that and you're half assing it.

Would five cases last two or three days?

Ask me how I know that! :D My first apartment I grabbed a box of Fixall out of my dad's garage thinking it was drywall mud... it was not pretty.

No not the same thing. Fixall really do not shrink, that much:rolleyes: (does not matter in your situation) like other "mud". Its much stronger.

Now that is the best solution I've heard yet!!

I make no promises. I get REALLY thirsty when I'm finishing drywall. You know with all that powder you're mixing and then the dust from sanding you might have to go with 6 but if you're planning on drinking any you might have to bump that up a bit more :D